Shaft coupler



R. D. WOOD SHAFT COUPLER Oct. 9, 1962 Filed Jan. 24, 1.961

m m m RoBERT DARIUS Wool:

United States Patent 3,057,647 SHAFT COUPLER Robert Darius Wood, Athens, Ga., assignor to General Time Corporation, New York, N.Y., a corporation of Delaware Filed Jan. 24, 1961, Ser. No. 84,725 4 Claims. (Cl. 287-110) The present invention relates to a device and procedure for coupling small diameter shafts and it is more particularly concerned with such a coupling device and procedure for use in an electric clock timer mechanism.

The use of clock radios and other electrical timing devices has greatly increased in recent years. Incident to the proper use of these devices is the necessity for providing suitable control knobs and mechanism for manually setting the timer for subsequent automatic operation during the selected interval. In the past this has been accomplished by extending the time-set control shaft of the electric clock mechanism through the enclosure of the radio or timer and attaching a knob to the end of the shaft for manual setting.

In most cases the coupling of this extension to the timer has been achieved by theading the end of the timer shaft and the set knob shank to form a cooperating threaded connection. Alternatively, a sleeve and set screw coupler has been employed. However, in either case certain disadvantages have been encountered arising principally from breakage, twisting or back threading of the threaded connection, or slippage and failure of the sleeve coupler. In addition, since in either case a metallic coupler is employed, a short circuit in the timing device may cause curent to be communicated through the shaft, coupling device and extension to the set-knob raising the possibility of an electrical shock.

Accordingly, it is an important object of the present invention to provide an improved shaft coupling device which is inexpensive to manufacture, easy to install and dependable in operation.

More specifically, it is an object to provide such a coupling that securely holds the shaft ends in alinement and obviates looseness, slippage and mechanical failure of the components.

It is also an object to provide a coupling of the above type which is made of an insulating material, such as nylon, thus removing the possibility of unwanted conduction or electric shock.

An additional object is to provide a coupling of the above type which is inexpensive to make and use since it is easily and simply formed of a single piece of plastic material, can be installed without the use of special tools and can be used for a variety of applications.

Other objects and advantages of the invention will become apparent upon reading the attached detailed description and upon reference to the drawings in which:

FIGURE 1 is a perspective view showing a one piece plastic shaft coupler incorporating the features of the present invention;

FIG. 2 is an enlarged sectional view taken along the lines 2--2 of FIGURE 1;

FIG. 3 is an enlarged partial sectional view of the necked down Shearing portion of the shaft coupler;

FIG. 4 is a sectional view of the coupler with two small shafts inserted; and

FIG. 5 is a sectional view of the coupler after it has been telescopically collapsed to join the two inserted shafts.

While the invention will be described in connection with a preferred embodiment, it will be understood that I do not intend to limit the invention to that embodiment, but on the contrary, intend to cover alterations, modifications and equivalents as may be included within the spirit 3,057,647 Patented Oct. 9, 1962 r ce and scope of the invention as defined by the appended claims.

Turning first to FIG. 1, there is shown a one piece shaft coupling device 20 incorporating the features of the present invention. In the preferred embodiment, the coupler is illustrated as being made of nylon. However, it is understood that any similar plastic-type material might also be employed. This coupling device comprises a shaft receiving sleeve 21 adaptable to accommodate two axially alined shafts 22, 23 (as shown in FIG. 4), and an outer collar 24.

The shaft receiving sleeve 21 is shown here with a series of longitudinal slots 25 extending from one end substantially through the entire length. These slots thus separate the sleeve into a plurality of circumferentially spaced axially extending resilient fingers 26. Each of these fingers is formed with a projection 27 extending radially inward at substantially the midpoint. The two respective transverse surfaces 28, 29 of these projections 27 form an in ternal end wall or base defining two shaft receiving shells 3t 31.

Referring more particularly, to FIG. 4, it will be noted that when the two shafts 23-22 are inserted into the respective shells 3t}, 31, they come to rest against the surfaces 28, 29 of the projections 27. These projections thereby serve not only as a stop for the shaft ends, but also as a separator and insulator between the shafts. Attention is also directed to FIG. 5 in this regard, where it will be noted that the radially inward portion of the projections 27 terminate short of the center of the sleeve 21. This construction thereby allows each of the fingers 26 and its corresponding projection 27 to be radially moved independent of the others, for reasons which will become more readily apparent. 1

In accordance with the present invention, the outer collar 24 is formed so that it defines a cylinder of uniform bore 32 substantially the same length as the shaft receiving sleeve 21 and having an inner diameter slightly smaller than the outer diameter of the sleeve 21 so that when the collar is telescoped over the sleeve the fingers of the latter are moved into gripping relation with the shaft ends. Moreover, the collar is molded integral with the sleeve to form a one piece construction having intentionally shearable connecting sections.

Referring now to FIGS. 2 and 3, it will be seen that the fingers 26 are attached to the outer collar 24 by the respective connecting sections 33. More particularly, this connection section is formed of a limited cross sectional area defined by the beveled surfaces 34, 35 of the fingers 26, and the end plane 36 of the collar 24. It is obvious, therefore, that section 33, being more limited in cross sectional area than any other portion of the coupler and abruptly necked down, will be the point of failure under axial compression. Failure occurs by shearing along line 37.

When applying the coupler 20 to its intended purpose, the two shafts 23-22 are inserted into the respective shells 30, 31 so that they come to rest against the projections 27 (see FIG. 4). The beveled surface 35 guides the right hand shaft into seated position. At this time the collar 24 extends axially away from the sleeve 21 and centrally encompasses shaft 23. An axial force is then applied to the end 38 of the collar 24 tending to compress the collar and sleeve axially together. Since the section 33 joining the collar 24 and the sleeve 21 is of small cross section, it shears, and as the two members are compressed together, the beveled surface 34 at the end of the fingers acts as an entering wedge forcing the fingers inwardly and causing the outer collar 24 to expand slightly as it rides up on the surface 34 telescoping over the sleeve 21 in a force fit (see FIG. 5). As a result the not essential for the use of this novel coupling, greatly increases the gripping force of the flexible fingers 26. It may be seen that since the coupling is made of a plastic material the radially compressive force exerted on the fingers 26 by the collar 24 causes the fingers to mold themselves around the irregular surface of the shafts, thus enhancing the strength of the bond.

While the collar 24 is shown as having a uniform bore, the bore may be tapered providing that the fingers are tapered to about the same degree to provide uniform holding action at both ends of the resulting coupling.

I claim as my invention:

1. A one piece plastic shaft coupler for joining shafts end to end comprising, a shaft-engaging sleeve, said sleeve being longitudinally slotted to form a plurality of flexible finger-like members, each of said fingers having at its midpoint an offset portion extending radially inwardly forming an end stop or separation for each of two axially alined shafts inserted within said sleeve, a cylindrical collar coaxial with said sleeve joined at one end to the individual ends of said fingers at a region 'of reduced cross section, said collar being substantially the same length as said fingered sleeve with an inner diameter somewhat less than the outer diameter of said sleeve, and said reduced cross section being abruptly necked down for concentration of shearing stress when an axial force is applied to said collar, and at least one end of the collar and sleeve having a tapered surface adjoining the region of reducedcross section, so that said collar telescopes over said sleeve compressing said fingers into gripping engagement with the inserted shafts.

2. A one piece plastic shaft coupler for joining shafts end to end comprising, a shaft-engaging sleeve, said sleeve being longitudinally slotted to form a plurality of flexible finger-like members, a cylindrical collar coaxial with said sleeve joined at one end tothe individual ends of said fingers at a region of reduced cross section, said collar being substantially the same length as said fingered sleeve with an inner diameter somewhat less than the outer diameter of said sleeve, and said reduced cross section being abruptly necked down for concentration of shearing stress when an axial force is applied to said collar so that said collar telescopes over said sleeve compressing said fingers into gripping engagement with the inserted shafts.

3. A plastic coupler for joining shafts end to end comprising, a shaft receiving sleeve slotted the entire length to form a plurality of flexible fingers, said fingers each having an inwardly extending abutment at the center portion thereof separating said sleeve into first and second shaft receiving portions, a collar axially alined with said sleeve and of substantially the same length, said sleeve having an inside diameter slightly greater than the diameter of the shafts to be connected and having an outside diameter slightly greater than the internal diameter of the collar, said collar being connected end to end to said sleeve, which has a tapered endat the point of connection to the collar so that when force is applied to the end of the collar the latter telescopes over the sleeve and compresses said fingers into engagement with the respective ends of the shafts.

4. A plastic coupler for joining shafts end to end comprising, a shaft receiving sleeve slotted the entire length to form a plurality of flexible fingers, a collar axially alined with said sleeve and of substantially the same length, said sleeve having an inside diameter slightly greater than the diameter of the shafts to be connected and having an outside diameter slightly greater than the internal diameter of the collar, said collar being connected end to end to said sleeve and said sleeve having a tapered end at the point of connection to the collar so that when force is applied to the end of the collar the latter telescopes over the sleeve and compresses said fingers into engagement with the respective ends of the shafts.

References Cited in the file of this patent UNITED STATES PATENTS 1,786,717 Moore et al. Dec. 30, 1930 2,080,627 Morgan May 18, 1937 2,872,225 Walker Feb. 3, 1959 FOREIGN PATENTS 161,039 Australia Feb. 9, 1955 808,017 Germany July 9, 1951 974,884 France Oct, 4-, 1950 847,470 France July 3, 1939 997,611 France Sept. 12, 1951 

